How to compress the image ?

for example, I have a 3D image in grayscale, 512X512X300.

I just want to compress it in X and Y plane.

I want 4 pixels to combine into one pixel.

And the value of the combined pixel takes average on that 4 pixels or take its max.

Can I directly do on 3D image? If not, please tell me how to do it on 2D image.

Thanks.

Answer 1

[Image Analyst]

Just save it as a .mat file. This is a proprietary binary format that will probably be fairly compressed, and anyway, it will make it convenient to read back in to MATLAB.

[tabw]

Image Analyst,

You are saying I have to save every single 2D image in mat format, right? I guess I can't save 3D image directly,right?

After saving, How to compress in the way I want ?

combining 4pixel into 1 pixel. and How to control its value ?

[Image Analyst]

Just save the whole variable. If the variable is a 3D array, save that.

save(filename, 'array3d');

[tabw]

And then?What should I do next? I guess it is not to use imresize this function to compress ,right?

[Image Analyst]

No you don't use imresize(). That changes the number of rows and columns in the image. save() saves the image to disk with fewer bytes than when it's loaded into memory, or saved to disk with a sequence of uncompressed 2D images. I have no idea what you want to do after that - you didn't say. All you said is you want to compress it (not resize it - they're very very different).

[tabw]

I should state more clearly.

I want to compress the pixel size. maybe say in this way, I want to combine 4 pixels into 1 pixel because my image is too big.

[Image Analyst]

Then use imresize().

Answer 2

[Yawar Rehman]

image analyst is rigth, i think you have a stack 300 gray scale images whose dimensions are 512x512.

compression usually involves techniques like principal components analysis. but from your question it is more evident that you want to downsample an image by the factor of 1/4 rather than compress. i think this would be useful!

% images you have
imgs = zeros(512,512,300);
% downsample by 1/4
downImages = imresize(imgs,1/4);